High energy radiation processing of EPDM in hydrocarbon environment

Different pressures of polypropylene (up to 1 atm), various doses (the maximum dose is 100 kGy), dose rate of 0.4 kGy/h, were applied to the EPDM dumbs and films. On the low dose range, polymer was subjected to a crosslinking process by which mechanical properties and chemical resistance are augmented. The higher dose exceeding 75 kGy brings about a decrease in thermal stability of irradiated samples due to the increase in the number of tertiary and quaternary carbon atoms. The medium pressure of propylene, around 0.7 atm, becomes the most suitable processing parameter, which is convenient for high yield of crosslinking. The mechanical measurements applied to irradiated EPDM samples emphasise the beneficial action of hydrocarbon surrounding. The ability of high energy radiation to promote structural modifications in EPDM is the lack of competition between the reactivity of free radicals with other hydrocarbon intermediates and with oxygen. The evolution in the thermal stability of EPDM specimens was determined by oxygen uptake method, which depicts the behaviour of radiation-processed elastomer under hard application condition. The kinetic parameters of thermal oxidation, oxidation induction time and oxidation rate, indicate the efficiency of low dose exposure on ethylene-propylene diene terpolymer. The consequence of the application of radiochemical method for the enlarging service duration is the decrease in the oxygen diffusion into polymer bulk and, thus, the decrease in the oxidative oxidation rate. (author)